CVE-2020-29483 : Security Advisory and Response

An issue was discovered in Xen through 4.14.x where xenstored and guests communicate via a shared memory page using a specific protocol. Violations of this protocol can lead to serious consequences.

Understanding CVE-2020-29483

This CVE highlights a vulnerability in Xen that can be exploited by malicious guests to cause denial of service attacks.

What is CVE-2020-29483?

The issue arises when a guest violates the communication protocol with xenstored, leading to improper handling by xenstored, potentially resulting in a crash or denial of service.

The Impact of CVE-2020-29483

Malicious guests can block host resources even after their termination, causing a denial of service.
A vulnerability in xenstored can be exploited by guests with a stub domain device model, potentially leading to a crash.

Technical Details of CVE-2020-29483

This section provides more in-depth technical insights into the vulnerability.

Vulnerability Description

Xenstored drops connections to guests violating the protocol, but the handling can lead to a zombie domain and resource blocking.

Affected Systems and Versions

Only the C variant of Xenstore is affected; the Ocaml variant is not vulnerable.
HVM guests with a stubdom device model can trigger a serious denial of service.

Exploitation Mechanism

Violation of the Xenstore protocol by guests running in a stub-domain can lead to a use-after-free scenario in xenstored, potentially causing a crash.

Mitigation and Prevention

Protecting systems from this vulnerability requires immediate actions and long-term security practices.

Immediate Steps to Take

Apply patches provided by Xen to address the vulnerability.
Monitor system resources for any unusual activity that could indicate a potential exploit.

Long-Term Security Practices

Regularly update Xen and related components to ensure the latest security fixes are in place.
Implement network segmentation to limit the impact of potential attacks.

Patching and Updates

Stay informed about security advisories from Xen and promptly apply patches to mitigate risks.